Carbon nanomaterials produced from heavy oil fractions and method for producing same

ABSTRACT

The present invention relates to a method for producing carbon nanoparticles from heavy petroleum fractions as the carbon source (precursor), particularly aromatic oil residue (RARO) by chemical vapor deposition (CVD), and optionally by using an organometallic catalyst that is soluble in the precursor. The main feature of the method according to the invention is that the precursor is evaporated in a controlled manner so as to provide a pulse supply of precursor having a constant composition to the inside of a tubular furnace which can be arranged in a vertical position for the continuous production of nanomaterials or in a horizontal position for batch production.

FIELD OF THE INVENTION

The present invention relates to a process for obtaining carbon nanoparticles, from heavy petroleum fractions as carbon source (precursor), particularly aromatic oil residue, using the technique of chemical vapor deposition (CVD—Chemical Vapor Deposition) in the presence of an organometallic catalyst soluble in the precursor.

RELATED TECHNIQUE

Carbon nanotubes (CNT) are a new class of materials discovered in 1991 by Sumio Iijima and exhibit extraordinary mechanical, electrical and thermal properties, having the highest strength tensile known, the order of 200 GPa, 100 times more resistant than the steel with only one sixth of its density.

Several processes have been developed for the synthesis of these materials, mainly by the main discharge between graphite electrodes and by Chemical Vapor Deposition in the presence of a catalyst. The latter has the greatest potential for mass production of nanotubes. Catalysts are used as transition metals such as Fe, Ni and Co or its oxides. An example of this process is described in U.S. Pat. No. 7,338,648 of Apr. 3, 2008, according to which carbon nanotubes are obtained by the flow of methane over a catalyst of Fe/Mo supported on alumina, in an inert gas atmosphere.

Carbon nanospheres have also been obtained from a variety of pure hydrocarbons (solid, liquid or gas), using this technique, with and without catalyst, as shown in Miao, J. et al. Carbon, 2004, 42, 813-822; Serp, R. K. P. et al. Carbon, 2001, 39, 615-628; Sharon M. et al. Carbon, 1998, 36, 507-511; Jin, Y. et al. Carbon, 2005, 43, 1944-1953; Qian, H. et al. Carbon, 2004, 42, 761-766, cited here as reference. The hydrocarbon precursor is typically fed into the gas phase to a tubular furnace under inert atmosphere, affecting the nucleation and formation of nanospheres under certain appropriate conditions.

The production of carbon nanomaterials (nanospheres and nanofilaments) by the process of chemical vapor deposition is well established in the literature from different hydrocarbon gases (such as methane and acetylene) [Baker, RTK—Catalytic growth of carbon filaments—Carbon 27, 315-323, 1989; Levesque, A. et al. Monodisperse—Carbon nanopearls in a foam-like arrangement: a new carbon nano-compound for cold cathodes—Thin Solid Films 464-465, 308-314, 2004], liquids (such as benzene, toluene and xylene) [Endo, M.—Grow carbon in the vapor phase—Chemtech 18, 568-576, 1988 Jin, YZ et al.—Large-scale synthesis and Characterization of carbon spheres prepared by direct pyrolysis of hydrocarbons—Carbon 43, 1944-1953, 2005], and solids (such as camphor) [Sharon, M. et al.—Spongy carbon nanobeads: a new material—Carbon 36, 507-511, 1998; Musso, S. et al.—Growth of macroscopic carbon nanotube mats and Their mechanical properties—Carbon 45, 1133-1136, 2007].

Asphalt has been used in the production of nanospheres without catalysts [Liu, X. et al.—Fuel Processing Technology 87 (2006) 919-925] but because it is a solid material it involves practical difficulties in feeding continuous and controlled process.

The use of mixtures of hydrocarbons in the production of nanospheres is potentially advantageous for allowing the use of cheaper raw materials and lower value added, but very few have succeeded.

The use of mixtures of hydrocarbons as precursors, especially those derived from petroleum, was successful only from light fractions and easy steaming, like kerosene [Kumar, M. et al.—Synthesis of conducting fibers, nanotubes and thin films of carbon from commercial kerosene—Materials Research Bulletin 34, 791-801, 1999] and solid products such as asphalt [Liu, X. et al.—Deoiled asphalt carbon source for the Preparation of Various carbon materials by chemical vapor deposition—Fuel Processing Technology 87, 919-925, 2006; Yang, Y. et al.—Preparation of vapor-grown carbon fibers from deoiled asphalt—Carbon 44, 1661-1664, 2006].

However, some drawbacks can be observed immediately. The lighter fractions of petroleum have wide commercial application, so their use would bring an added value in the process greatly reduced. Moreover, the use of a solid precursor presents a series of practical difficulties, both to maintain a continuous supply and to control the composition fed to the process.

The aim of the present invention is the use of heavy petroleum fractions as feedstock for the production of carbon nanomaterials (nanospheres and nanofilaments), to allow both to reduce the cost of these materials and add value to the oil fractions of low commercial value. However, since they are liquids with high viscosity and low volatility, these fractions can not be fed to the process by methods commonly employed in the technique: simple vaporization or aerosol formation.

SUMMARY OF THE INVENTION

The present invention relates to the production of carbon nanomaterials, using the technique of chemical vapor deposition, using as feedstock heavy oil fractions obtained directly from its refining or processing of an oil product to other purposes.

Other liquid feedstocks derived from petroleum, subject to vaporization can also be used as feedstock in the process.

The proposed process employs an apparatus specially adapted for its intended purpose, and can operate continuously or in batch, using vertical or horizontal tubular furnace, and, briefly, the process comprises the following steps:

-   -   a) Vaporize a controlled precursor, which may contain dissolved         therein an organometallic catalyst, so as to provide pulses         having a constant composition into the reaction chamber of a         tubular furnace;     -   b) Nanomaterials form from the decomposition of hydrocarbons, as         its vapor is swept by an inert gas flow into the interior of a         tube of alumina contained in a tubular furnace maintained at a         temperature between 700° C. and 1200° C.;     -   c) Collect the product continuously, when using a vertical         tubular furnace, or in batch when using a horizontal tubular         furnace, said apparatus optionally provided with a particle         retention system connected in the furnace outlet.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 shows a schematic representation of apparatus used for undertaking the process of invention.

FIG. 2 shows in enlarged scale of the carbon nanospheres obtained on a quartz substrate.

FIG. 3 illustrates schematically the contact configuration for the equipment used for tribological evaluation of carbon nanospheres.

FIG. 4 shows a graph with the results of increased friction strenght comparison between the prepared oils with carbon nanospheres and a sample of commercial oil.

FIG. 5 shows a graph with the temperature profiles for nanospheres prepared with oils.

DETAILED DESCRIPTION OF THE INVENTION

In order to make the process of the invention better understood, it will described in detail. It must be remembered, however, that the examples provided are illustrative purposes only and should not limit the invention.

It was found that a liquid residue obtained as a byproduct of petroleum pitches production from decant oil can be successfully employed for the production of carbon nanospheres with high purity, by CVD technique, without the use of catalysts.

This means that the disposal of such liquid residue is no longer an environmental problem, since in addition to using the residue as a raw material, there is still the economic advantage of allowing the combination of production processes and the obtaining of carbon nanospheres.

Liquid residual oil are therefore an advantageous source for production of carbon nanospheres, since, besides its low cost, have high carbon content (around 90% for samples of decant oil) it is obtained in large quantities in the processes of petroleum refining.

The process of obtaining nanospheres, object of the present invention basically consists of:

-   a) Vaporize the precursor in a controlled manner so as to provide     pulses of vapor having constant composition into the reaction     chamber of a tubular furnace; -   b) Contain optionally an organometallic catalyst, such as ferrocene,     dissolved in the precursor; -   c) Produce nanomaterials from the decomposition of hydrocarbons, as     the vapor is swept by an inert gas flow into the interior of a tube     of alumina contained in a tubular furnace and maintained at a     temperature between 700° C. and 1200° C.; -   d) Collect the product in a suitable container, being the tubular     furnace optionally provided with a particle retention system in the     outlet; -   e) Collect the product continuously from the bottom of the tubular     furnace in a vertical position; -   f) Collect the product in batch, by leaving the tubular furnace,     when in a horizontal position.

The production of nanospheres is accomplished by the vaporization of residual oil, which is sent to the interior of a tubular furnace, kept at temperatures between 700° C. and 1200° C., preferably between 800° C. and 1100° C. by a controlled flow of inert gas, typically nitrogen.

In FIG. 1 accompanying this report, it is illustrated schematically the apparatus adopting the vertical position used for the development of the present invention, for applying the process continuously. The arrangement includes a vertical furnace (1) having inside a tube of alumina (2), at its upper end being connected to a heating chamber (3), and at its lower end to a device (4) for collection nanoparticles. In the heating chamber (3) are connected to a source of inert gas (5), provided with adequate flow controllers, and a supply of precursor (6), provided with adequate means of measurement, such as a peristaltic pump (7). In the output of device (4) the retention of nanoparticles may additionally be adapted to a particle retention system (8).

The vertical furnace allows the product to be collected by gravity, so the process can be operated continuously.

According to prior art, the liquid precursors used in CVD processes are generally vaporized by the bubbling of inert gas in the precursor or by injecting the liquid in the gas stream, or by simple heating of a quantity of precursor (batch). In the case of the present invention the first two methods can not be applied, first due to the high viscosity of the residue applied, and second because it is a mixture of hydrocarbons, for the simple heating of a quantity of material would lead to changes in the composition gas phase during the process.

So, what is now proposed to solve the problem is to pump the residue to the interior of a heating chamber (3), where it is dripped onto a surface maintained at a temperature high enough to vaporize all at once all drops of the feedstock.

It is worth remembering that drip feed has already been suggested in studies of production nanofilaments, but with the direct injection of the droplets inside the reactor through a capillary needle, and in order to optimize the productivity of the catalyst used (Fe or Ni), where kerosene was used as raw material, material whose properties are quite different chemical characteristics of heavy petroleum fractions.

A typical catalyst employed in the production of nanofilamentos is ferrocene [Fe (C2H5) 2], becoming the precursor to the simultaneous vaporization (floating catalyst method), since it is soluble in the waste employees. This technique can, therefore, similar to that observed with the use of asphalt [Liu, X. et al.—Deoiled asphalt carbon source for the Preparation of Various carbon materials by chemical vapor deposition—Fuel Processing Technology 87, 919-925, 2006], also be employed in the production of nanofilamentos from heavy fractions of petroleum.

According to the process of the present invention the precursor may be vaporized in a controlled manner, with the help, for example, a peristaltic pump (7) and means of controlling the flow of inert gas (5), to provide a feed pulses of constant composition in the tubular furnace where the production of nanomaterials occurs. The precursor (6) is continuously pumped to a vaporization chamber (3), in which it is dripped onto a surface (not detailed in the Figure) heated to a temperature high enough to ensure its complete vaporization, simultaneously being swept by a inert gas flow (5) into the tubular furnace (1).

If nanofilaments are to be produced, a suitable organometallic catalyst such as ferrocene, should be dissolved in the precursor, so as to enable the creation of centers of growth of these nanofilaments.

Inside the tubular furnace (1) the alumina (2) tube is maintained at a temperature between 700° C. and 1200° C., preferably between 800° C. and 1000° C., where hydrocarbons decomposition occurs with the production of nanomaterial whose properties depend on temperature, residence time, concentration of precursor in the gas flow, and catalyst concentration if used.

If the tubular furnace (1) is vertical the product can be collected continuously in a device (4) from the lower end of the tube (2). If the oven is operated in a horizontal position, the product can be obtained in batch and, if desired, on a suitable substrate. This will allow to be obtained various types of nanomaterials, such as nanotubes, nanofibers and other nanofilamentos, nanofilms, laminates, among others.

In any case, as the product has extremely low density, it is desirable to adapt a system for retention (8) of the material in the kiln, thereby avoiding particles swept by the flow of gas.

To better evaluate the process of preparation of nanomaterials, the object of this invention, illustrative examples are presented below, which, however, should not limit the invention. Similarly, the evaluation of the properties of nanospheres obtained by the process of the invention will also be presented in na illustrative example.

Process of Preparing Nanospheres Example 1

In a horizontal tubular furnace with an alumina tube of about 5 cm (2 inches) internal diameter, kept at 1200° C., a decanted oil was fed at a flow rate of 7 mL/h in a stream of nitrogen 1 L/min for 30 min. Carbon nanospheres were obtained on a quartz substrate, and FIG. 2 shows a amplified scaled the nanospheres obtained. In the absence of a particle retention system, 0.046 g of material was collected, and most of it was swept by the gas flow.

Example 2

In a vertical tubular furnace with an alumina tube of about 5 cm (2 inches) internal diameter, kept at 1100° C., a decanted oil was fed at a flow rate of 15 mL/h with a flow of argon at 4 L/min for 120 min. On the output of the furnace a particle retention system was adapted, and 13.1 g of carbon nanospheres were collected.

Tribology Evaluation of Carbon Nanospheres Example 3

The carbon nanospheres can be used for tribological purposes, in order to reduce friction and wear between two surfaces in mechanical contact. Currently, new high-performance lubricants have been developed in order to obtain an increase in energy efficiency.

For the evaluation of friction and wear, it was compared a commercial automotive oil for internal combustion engines, and specification API SL SAE 20W50, with another of the same viscosity grade, made of only the base oil and the carbon nanospheres obtained according to the invention.

The equipment used in the test was a four ball tribometer (ball four), whose mechanism of operation is shown schematically in FIG. 3.

In this equipment, three balls are fixed within a reservoir, which adds lubricant to be tested. A fourth ball is fixed on the movable shaft of an electric motor. Initially, it was applied a load between the three spheres and other movable property and controls the temperature of the oil bath in the desired condition.

The electric motor is activated and controls the rotation also in the level of interest. After stabilizing all values of the parameters, a clutch is powered and start a rapid transmission of movement between the spheres in contact.

The oils with the addition of the carbon nanospheres were prepared with the 0.05%, 0.10%, 0.35% and 0.50% concentration of nanosphere. A load of 40 kgf, rotation of 1500 rpm, and initial temperature of 60 C were applied (after the test started, the temperature controller was turned off and the thermal evolution in the oil bath was monitored due to friction between surfaces under contact) lasting 30 minutes. The scars of wear, the friction strength and temperature profile were measured during the tests.

FIG. 4 presents the results of increased friction strength comparison between the prepared oils with carbon nanospheres and the commercial oil.

One can observe a significant reduction of friction in comparison with the commercial oil. The highest performance for the oil prepared with the lowest concentration of nanospheres may suggest that the mechanism of action between the surfaces in contact, is by rolling the nanospheres.

FIG. 5 shows the temperature profiles for nanospheres prepared with oils.

It may be noted that the final temperature was the lowest of all for the oil formulated with the lowest concentration of nanospheres. The highest end temperature was reached by the commercial oil. This behavior shows that oils formulated with carbon nanospheres can lead to greater energy efficiencies, which is a major issue at present for dynamic equipment. 

1. METHOD FOR PRODUCING CARBON NANOMATERIALS, characterized by employing as feedstock heavy oil fractions obtained directly from its refining or processing of an oil product for other purposes, using the technique of chemical vapor deposition to obtain carbon nanospheres and nanofilaments.
 2. METHOD FOR PRODUCING CARBON NANOMATERIALS according to claim 1, characterized by comprising the steps of: a) Vaporize a precursor, so as to provide pulses having constant composition into a reaction chamber of a tubular furnace where the reaction occurs for the production of nanomaterials, the precursor being pumped continuously to a vaporization chamber, where is dripped onto a surface heated to a temperature high enough to ensure its complete vaporization, then being swept by a flow of inert gas into the furnace; b) Decomposition of the precursor, as its vapor is swept by an inert gas flow into the interior of a tube of alumina contained inside the tubular furnace, maintained at a temperature between 700° C. and 1200° C. and preferably between 800° C. and 1100° C., where occurs the decomposition and production of carbon nanomaterial; c) Collect the product in a device coupled to the output of that tubular furnace, which is optionally fitted with a particle retention system.
 3. METHOD FOR PRODUCING CARBON NANOMATERIALS according to claim 1, characterized by producing carbon nanofilaments precursor dissolved in a suitable organometallic catalyst, such as ferrocene.
 4. METHOD FOR PRODUCING CARBON NANOMATERIALS according to claim 1, characterized by continuous production, when using the tubular furnace in a vertical position, collecting nanoparticles by gravity from the bottom of the tubular furnace to a device, the furnace exit being connected to a particle retaition system.
 5. METHOD FOR PRODUCING CARBON NANOMATERIALS according to claim 1, characterized by batch production when using the tubular furnace with in a horizontal position, collecting nanoparticles to a device of payment, the furnace exit being connected to a particle retention system.
 6. CARBON NANOMATERIALS, characterized by being obtained from heavy petroleum fractions as carbon source, from its refining or processing of an oil product for other purposes, using the technique of chemical vapor deposition, whereby the precursor is vaporized in a controlled manner so as to provide pulses having constant composition to the interior of a tubular furnace, the precursor being pumped continuously to a vaporization chamber, where is dripped onto a surface heated to a temperature high enough to ensure its complete vaporization, and simultaneously being swept by a flow of inert gas into the interior of the tubular furnace.
 7. CARBON NANOMATERIALS according to claim 6, characterized as being carbon nanospheres.
 8. CARBON NANOMATERIALS according to claim 6, characterized as being carbon nanofilaments.
 9. CARBON NANOMATERIALS according to claim 6, characterized as nanospheres produced without the use of catalyst.
 10. CARBON NANOMATERIALS according to claim 6, characterized as nanofilaments produced by dissolving the precursor into a suitable organometallic catalyst, such as ferrocene. 